The ERD as a Communication Tool

I teach a college course at the University of Washington, and as part of the class I include a series on creating a using an Entity Relationship Diagram, or ERD. An ERD, as I’m sure most of you know, is a series of box and connector shapes that explain how a database is laid out. I was asked recently by a DBA as to whether I really used ERDs, and if they were really effective.

I think that they are – if they are used properly. An ERD is the way I talk to the business and the developers about the data store. Granted, I normally use the Logical ERD for this purpose, and I don’t show the entire data structure if the system is large and complex, and I don’t always create a physical ERD. But this tool, like any graphical representation, helps me speak to a group quickly to get my meaning across.

The trouble I’ve had lately is sending the ERD in a format that everyone can read. The picture is easy enough, but the detail is a little harder. Visio no longer has a good ERD report, and I can’t expect that everyone has that program or will download the viewer, even though it is free. And other programs, such as ERWin, are prohibitively expensive for a lot of folks, especially if they don’t do design work that often.

For now I’m using the Database Designer in SQL Server Management Studio, which is far from ideal. It doesn’t conform to any ERD standards, but I can turn on the type and description columns, show the relationships in text, and then I copy that to the clipboard and send it around. Not optimal, but at least partly portable. Of course, this is a physical view, but when I show the columns, types and descriptions (I use extended properties a lot) it looks fairly logical.